Question

From the following list of elements-Ar, H, Ga, Al, Ca, Br, \(\mathrm{Ge}, \mathrm{K}, \mathrm{O}\) - pick the one that best fits each description. Use each element only once: (a) an alkali metal, (b) an alkaline earth metal, (c) a noble gas, (d) a halogen, (e) a metalloid, (f) a nonmetal listed in group \(1 \mathrm{~A},(\mathrm{~g})\) a metal that forms a \(3+\) ion, (h) a nonmetal that forms a \(2-\) ion, (i) an element that resembles aluminum.

Short answer

The elements corresponding to each description are: (a) K, (b) Ca, (c) Ar, (d) Br, (e) Ge, (f) H, (g) Al, (h) O, (i) Ga.

Step-by-step solution

Identify the elements in the periodic table

First, locate each element in the periodic table and identify the group it belongs to, as well as its properties.

Pick the alkali metal

Alkali metals belong to Group 1 of the periodic table. From the list, the only element from Group 1 is Potassium (K). So, (a) an alkali metal is K.

Pick the alkaline earth metal

Alkaline earth metals belong to Group 2 of the periodic table. From the list, the only element from Group 2 is Calcium (Ca). So, (b) an alkaline earth metal is Ca.

Pick the noble gas

Noble gases belong to Group 18 (or group 8A) of the periodic table. From the list, the only noble gas is Argon (Ar). So, (c) a noble gas is Ar.

Pick the halogen

Halogens belong to Group 17 (or group 7A) of the periodic table. From the list, the only halogen is Bromine (Br). So, (d) a halogen is Br.

Pick the metalloid

Metalloids are elements that share properties of both metals and non-metals. From the list, the only metalloid is Germanium (Ge). So, (e) a metalloid is Ge.

Pick the nonmetal in group 1A

In this case, we are looking for a nonmetal in Group 1 of the periodic table. From the list, the only nonmetal listed in Group 1 is Hydrogen (H). So, (f) a nonmetal listed in group 1A is H.

Pick the metal that forms a 3+ ion

Both Aluminum (Al) and Gallium (Ga) are in Group 13 (or group 3A) and form 3+ ions. Since we are asked to pick only one, we will choose Aluminum (Al). So, (g) a metal that forms a 3+ ion is Al.

Pick the nonmetal that forms a 2- ion

Oxygen (O) is a nonmetal from the list that forms a 2- ion. So, (h) a nonmetal that forms a 2- ion is O.

Pick the element that resembles Aluminum

Gallium (Ga) is an element that resembles Aluminum in chemical properties, as it is in the same group (Group 13) and has similar characteristics. So, (i) an element that resembles Aluminum is Ga. In conclusion, the elements corresponding to each description are: (a) K (b) Ca (c) Ar (d) Br (e) Ge (f) H (g) Al (h) O (i) Ga

Key concepts

Alkali Metal

Alkali metals are located in Group 1 of the periodic table. These elements, which include lithium, sodium, and potassium, are known for being highly reactive, especially with water, to form hydroxides. As the step-by-step solution indicates, potassium (K) is the alkali metal from the given list. It's noteworthy that all alkali metals have a single electron in their outer shell, leading them to easily lose this electron to form a +1 ion during chemical reactions.

When teaching about alkali metals, it's important to stress that their reactivity increases as you move down the group, with cesium and francium being the most reactive. Additionally, due to their reactivity, alkali metals are never found in their elemental form in nature.

Alkaline Earth Metal

Group 2 of the periodic table is home to the alkaline earth metals, including beryllium, magnesium, calcium, and others. These elements are characterized by having two electrons in their outermost shell, which they tend to lose to form +2 ions. Calcium (Ca) is identified in the solution as the alkaline earth metal from the provided elements list. It's also important to clarify that these metals are somewhat reactive but not as much as alkali metals because losing two electrons is less energetically favorable than losing one.

For educational purposes, highlighting that alkaline earth metals are commonly found in minerals within the earth's crust and have a higher melting point than alkali metals can help students understand their distinct properties.

Noble Gas

Noble gases make up Group 18 (or 8A) of the periodic table and are renowned for their low reactivity. These gases, which include helium, neon, argon, among others, have filled outer shells, making them chemically inert under standard conditions. Argon (Ar), as provided in the solution, is a noble gas that is used to illustrate this group's properties. It's significant to convey the uses of noble gases due to their non-reactivity, such as in lighting, welding, and as an atmosphere for chemical reactions where other gases might interfere.

When teaching, it’s also insightful to mention that helium has a filled shell with only two electrons because it follows the duet rule, rather than the octet rule seen in the other noble gases.

Halogen

Halogens are found in Group 17 (7A) of the periodic table and are known for being very reactive. These nonmetals, including fluorine, chlorine, bromine, and iodine, have seven electrons in their outer shells, which predisposes them to gain one additional electron to achieve a stable electron configuration. Bromine (Br) from the list is a halogen and a perfect example of these highly reactive elements. For educational content, emphasizing the destructive reactions of halogens with metals, which often result in salts, can be particularly interesting.

Furthermore, students should understand the concepts of electronegativity and oxidizing ability when studying halogens, as these are key to the group's reactive nature.

Metalloid

Metalloids are elements that display characteristics intermediate between metals and nonmetals. They are found along the stair-step line of the periodic table. Germanium (Ge) is the metalloid selected from the options. Metalloids like germanium have mixed properties, such as semiconductivity, which is valuable in electronics. Since they have the ability to conduct electricity, they are widely used in semiconductors and computer chips.

It's beneficial for students to learn about the versatility of metalloids in various applications, which can range from electronics to biomedicine, highlighting their importance in modern technology.

Nonmetal

Nonmetals are diverse in their properties and are found in different groups on the right side of the periodic table. They generally lack the luster, malleability, and electrical conductivity of metals. Hydrogen (H), being the nonmetal in group 1A as per our exercise, is unique as it's the simplest and most abundant element in the universe. While often associated with alkali metals due to its position in the table, its properties align it more closely with nonmetals.

When discussing nonmetals, it's crucial to mention that they can form both molecular and network covalent bonds, resulting in a wide array of physical properties, from gasses like neon to solids like carbon.

Ion Formation

Ion formation occurs when atoms gain or lose electrons to achieve a full valence shell, forming charged particles known as ions. The transformation into ions allows atoms to achieve more stable electronic configurations. Typically, metals lose electrons to form cations, while nonmetals gain electrons to form anions. The exercise shows examples like aluminum (Al) losing three electrons to form a 3+ ion and oxygen (O) gaining two electrons to form a 2- ion.

For teaching, it's essential to discuss trends in ionization energy and electron affinity as they relate to ion formation, helping students understand why certain elements tend to gain or lose specific numbers of electrons.

Chemical Properties

Chemical properties of elements are innate characteristics that determine how an element can chemically react with other substances. These include reactivity with water, acid-base behavior, and tendencies to form certain types of compounds. For instance, alkali metals react vigorously with water while noble gases are largely unreactive. It’s important to link each element's position on the periodic table to its chemical properties, as these are often related to their electron configurations.

Students should learn that understanding chemical properties is crucial for predicting the behavior of substances during chemical reactions and for the synthesis of new compounds in the laboratory.

Group Classification in Periodic Table

The group classification in the periodic table organizes elements into columns based on their valence electron configurations, which typically results in similar chemical and physical properties. Groups are often referred to by number, such as Group 1 for alkali metals or Group 17 for halogens, and sometimes by specific names. Understanding group classification helps to predict and understand element behavior and reactions.

When teaching the periodic table, it's imperative to emphasize that the position of an element not only determines the type of element (metal, nonmetal, or metalloid) but also provides insights into trends in reactivity, melting and boiling points, and atomic size.